Is the problem with the camera zoom fixed?
Depends what you mean by fixed. Since v3.1.2, the camera zoom works again but repeatedly zooming 4-5x makes the camera app crash. Same with v3.1.3. But in normal condition it is at least serviceable.
Do you know if this is a Murena problem or a Fairphone problem?
I did not experience this, not sure if I have 3.1.2 or 3.1.3 (community build).
3.1.3 was just a fix for SIM problem
In fact the digital zoom was first “fixed” in v3.1.1 (see release notes). But v3.1.1 never made it to the official channel for FP6. So the first official version that got working zoom was v.3.1.2, but that one introduced other issues (non-zoom related) which were then partly fixed in v3.1.3. I’m only talking about official builds. Don’t know much about community but maybe it got v3.1.1, unlike official.
This was an /e/OS software bug but it has been “fixed” since v3.1.1.